Variable resistor



H. G. RICHTER -VARIABLE gEsIsTQR Filed Jan. 16, 1935 June 2s, 1938.

lNvENToR ATTORNEYS Patented June 1.938

UNITED STATES PATENT ori-ica 2,121,933 vaarsnmassrs'ron Henry G. Richter, wennen, N. J. Application January 16, 1935, Serial No.2,001

llClaims.

This invention relates to variable resistors, and more particularly to moderately high resistance units of the wire-wound type.

The primary object of my invention is to generally improve wire-wound ,resistance elements.

A more specific object of my invention isv to provide a construction which will hold the resistance wire windings tightly in place ,even when dealing with fine wire wound at close pitch. Another object is to obtain good electrical contact between the resistance wire and appropriate soldering lugs without soldering and while using a minimum o! simpliiled parts.

It is common practice. particularly with radio apparatus and the like, to associate a power switch with the resistor, said power switch being actuated during the ilrst part of the movement of the control shaft of the resistor. It is desirable to actuate the power switch before rather than during resistance variation, which is best accomplished by'elongating the short-circuited or terminal part of the resistance element. and the fulillment of this desideratum constitutes another object of my invention.

It is sometimes sought to taper or step *the rate. or resistance variation, but this has been dimcult to accomplish when dealing with wirewound units. In accordance with a further object of my invention, I make it possible to step the resistance variation by simplified means, both this and the preceding object being accomplished while using standardized production parts similar to those used with a simple unit not having vthe features in question.

Still another object-of my invention is to facilitate the production of tandem resistance units,

that is, two or more independent units assembledinto a single compact( structure and controlled by a single control shaft. A further object of my y invention is to so design the resistor that the casing of the unit may be interchangeably closed by a simple back or'closure plate or a power switch lor one or more tandem resistor units. Still another object of my invention is to make many of the parts of the resistor unit inter` changeable with those used in a illm type resistor and their relation one'to the other, as are herein.

after more particularly described in the specication and sought to be deilned in the claims.

(c1. zotssi The specification is accompanied by a drawing in which:

Fig. 1 is a rear elevation of a resistor unit with the closure plate removed;

Fig. 2 is a section taken in the plane of the 5 line 2-2 of Fig. l with the closure plate in place;

Flg.3 is a section taken in the plane of the line I-I of Fig. l;

Fig. 4 is a perspective view' of an annular insulation plug forming a part of the resistor assembly;

Fig. 5 is a side elevation showing the manner in which units may be assembled in tandem;

Fig. 6 is a front elevation of the second or added unit shown in Fig. 5;

Fig. 'I is a side elevation showing the manner in which a power switch may be used for closing the resistor; I

' Fig. 8 is a front elevation of the power switch closure; and

Fig. 9 schematically illustrates an annular closure plug modified for a tapered or stepped wire-wound unit. .v l.

Referring to the drawing and more particularly to Figs. 1 through 4 thereof, the resistor comprises a preferably cylindrical casing i1 having a side wall i4 and a front end wall I6, the opposite end of the casing being left open. As here illustrated, the casingv is molded out of a single piece of insulation, but it may be formed of metal lined with insulation. The resistance is formed by an appropriate resistanceywire Il wound on a strip of insulation. 2l. Ittis convenient to make the strip 20 bendable. the resistance windings being applied thereto whilethe strip is straight, whereupon the strip is bent into arcuate conilguration and inserted within' the casing I2. An annular insulation plug 22 is then forced! into the casing within the arcuately bent yresistance element. Soldering lugs 24. best shown in Figs. l and 3, are preliminarily -inserted in the casing, saidlugs being L-shaped and having their inner ends 26 bearing against the outside of the terminal portions of the resistance winding. The plug 22 is dimensioned for a force tit within the resistance element, and when'pressed axially into position serves the dual function of locking the individual resistance windings tightly inplace and of forcing the terminal parts-of the windings tightly against the soldering lugs, thereby insuring good contact without the necessity oi' soldering or other special precautions. The leading or approach edge of plug!! is preferably rounded or/and tapered slightly. as is indicated at 23 in Fig. 2. p

resistance is varied vby a sliding contact Il formed'at the-end of a preferably long resilient arm'Ilsecured-to a radial ann 32y mounted.. on Athe control shaft Arms Il and $2 are here illustrated as secured together by a tenon 38 on 60 movement.

arm 32 passing through arm l2 and riveted thereover. The inner end of arm 22 is pressed to form a dished hub 38 within which there is placed an insulation washer lli. The inner end of shaft Il is squared at 42 and receives a metallic washer M, an insulation washer It, hub 28 with its insulation washer I0, and a stop arm SII, these parts all being riveted tightly on shaft Il, as is indicated at 52. The hole in hub Il is, of course, made larger than the squared end 42, so that the entire contact arm assembly is insulatediy mounted on the control shaft.

Electrical connection with the contact arm is made through soldering lug". 'The inner end of this soldering lug forms a ring Il which surrounds insulation washer I8 and bears in an axial direction against the face of hub 2l. The ring 56 has struck thereon diametrically opposed teats 58 which ride on hub 3l. 'I'he soldering lug is formed of sheet metal sufficiently resilient to insure good electrical contact. It will be noted in Fig. 1 that soldering lug I4 enters casing I2 at the ends of the resistance element, thus avoiding contact with the resistance windings. The lug is preferably recessed into the end wall i6 of the casing, as is best shown at il in Fig. 2, in order not to interfere with proper seating of the resistance element. The lug is held in place by insulation plug 22. The latter is preferably recessed at t2 to insure proper registration of the parts, and this recess is occupied by a bend Il in soldering lug Il.

Control shaft 34 is carried by a threaded metallic bushing C8 whichisflanged at il and riveted to casing wall I 0 at 10. The shaft is held against axial movement by thrust washer Il at one end of the bushing, and a split thrust washer 12 sprung into a mating groove 1I on the control shaft at the other end of the bushing.

The resistor is completed by a preferably metallic closure plate 1B secured at the open end of the casing. Cylindrical casing wall Il is preierably recessed at'" to receive closure plate'l. The closure plate is circular except for a registration proiection Il which nts into a recess I2 on casing wall I4. While closure plate 1l is not shown in plan, the projection Il is similar to that shown on the switch closure in Fig. 8. A ring of insulating material I2 may be interposed between the closure plate and the casing when assembling the parts. The closure plate is held in place by a single assembly screw I4 which passes through the front wall I8 of the casing, then through a hole I8 in the plug 22, and finally is threaded into the closure plate at Il. This assembly screw Il is so located as not to interfere with the full desired range of movement of the contact arm I2.

Plate 10 has struck inwardly therefrom a stop lug B8 which cooperates with the store-mentioned stop arm l0 to limit the movement of the control shaft.

If desired, the resistor may be combined with a power switch by substituting a switch closure for the simple closure .plate heretofore described. Such an arrangement is shown in Figs. 7 and 8. The resistor R corresponds to thatV heretofore described. The switch closure S comprises a plate III having the same outline as closure plate 1l. This plate includes a registration lug Il and threaded hole I1, like those heretofore described. and a. stop lug 92 which allows for the switch The switch is mounted on plate Il, and electrical connection is made through soidering lugs 84. toggle type and is controlled by a rocker Il to The switch is preferably of the which are secured bearing surfaces 9| which project through a window Ill in plate 80. Bearing fingers 2l lie in the path of movement of stop arm l0, and the parts are so arranged that when the stop arm reaches its end position, the switch is turned loff, this being the condition of the parts shown in Fig. 8 in which the stop arm il is indicated by broken lines. It will be understood that when the resistor is turned from its end position, the switch is tripped during the nrst part of the movement.

To avoid having the switch tripped only after traversing part of the resistance element, I shortcircuit the resistance winding for an appreciable distance at the starting terminal. This is accompllshed in a convenient manner at minimum cost by coating a part of the periphery of plug 22 with metallic paint, as is indicated at |02 in Fig. 4. I prefer to use a non-oxidizing metal like silver. When plug 22 is forced into place, the resistance windings in contact with the silver coating |02 are short-circuited and rendered ineffective. 'I'he coating is dirnensioned to compensate for tripping of the power switch. This feature may be used. of course, only with units intended to be equipped with a power switch, but the expense is so slight that I flnd it more convenient to use the metallic coating il! on all units, thereby standardizing the resistance value and adapting all units for the addition of a power switch.

This general idea of coating the periphery of the plug 22 may also beV used to provide a socalled tapered resistance unit. that is., a unit in which the rate of change of the resistance is not uniform. Tapering is valuable and vhas been used with considerable success in film type resistance units but has been too costly for use in wirewound units. as by varying the pitch of the winding or changing the size or material of the resistance wire. In accordance with my invention, the plug 22 may have a part of the periphery coated with a very low resistance film i, as is indicated in Fig. 9. When such a plug is forced into contact with the wire windings, a part of the winding is changed to a compound wire and nlm type unit, thereby lowering the resistance value of part of the element while still retaining a current carrying capacity better than is attainable'with a simple film type resistor. The shortcircuiting terminal or metallic coating il2 may, of course, also be used.

A further feature of my invention concerns tandem units. Such units are troublesome to stock because of the variety of combinations required. I simplify this problem by adding one or more tandem units lin to the standard resistor R, as is indicated in Fig. 5. Instead of closing the back of resistor R with a closure disc or power switch, the unit I IllA is added which in turn is open at its back face and preferably made exactly like the back edge of the standard unit, so that the regular closure plate or power switch may in turn be used to close the casing of the tandem unit lili. The casing of unit Ill is molded like that of unit R except that the forward edge is stepped or shouldered at l|2 and provided with a locating projection Ill, so that the units will mate snugly together. 'I'he assembly screw i Il is approximately twice as long as before and passes through both units from end to end. Unit lill in Figs. 5 and. 6 is intended to generically represent a tandem unit of either film or wire-wound type. If wire wound, the internal mechanism of the unit is like that of unit R, the essential difference being that the bushing and control shaft of unit l I terminate at the unit, and the control shaft has riveted thereto a drive disc H8. This disc is slotted at |20, and the waste metal is bent outwardly to form bearing surfaces l2! dimensioned to receive the stop arm 5|! of unit R. Stop arm 50 then functions as a coupling rather than a stop arm, but the stop arm of unit H0 assumes the motion limiting function.

An important feature of the present invention resides in the fact that the external dimensions of casing l2, stop arm 50, disc Ill, closure plate 16, and switch S are identical with the corresponding dimensions in the film type unit shown in my copending application Serial No. 734,810 heretofore mentioned. This makesit possible not only to connect wire-wound units in tandem with one another and nlm type units in tandem with one another, but more important, to connect wire-wound and film type units in tandem. Such flexibility of combination is valuable in meeting the varied requirements which arise in practice. In Figs. 5 and 6 the tandem unit lill equally well represents a unit of the film type or of the wire-wound type. 'If desired, the first unit (replacing R) may be of the nlm type and the second unit of the wire-wound type.

It is believed that the mode of constructing and using, as well as the many advantages of my resistor, will be apparent from the foregoing detailed description thereof. The windings and soldering lugs are locked tightly in place and are held in good electrical contact by their assembly between an external ring and an internal plug.

This internal plug serves dual yfunctions in receiving a metallic coating for short-circuiting terrninal windings and in receiving a resistance or other conductive coating for tapering the resistance value. The assembly of tandem units is facilitated and the combination of wire-wound and lm type units made possible.' Many of the parts of the wire-wound unit are identical with parts used in a film type unit, thereby simplifying manufacture. Sliding contact is made at the side rather than the edge of the resistance element, thus presenting a larger surface for contact. The contact arm is long and readily yield able, making for smooth even control.

It will be apparent that while I have shown and described my invention in preferred forms, many changes and modifications 'may be made in the structures disclosed without departing from the spirit of the invention defined Ain the' following claims.

I claim:

1. A variable resistor comprising a one-piece casing having an end and a cylindrical side-wall, a bushing secured to said end, a control shaft passing through said bushing, an arcuately bent resilient contact arm mounted on said control shaft, an arcuate wire-wound resistance element placed inside the cylindrical wall of the casing, said resistance element being small in radial dimension but broad in axial dimension, saidy of the inner wall of said element in back of said plug, and a removable closure for closing the open back end of the casing.

2. A variable resistor comprising a-cylindrical casing closed at one end, a bushing secured to said end, a control shaft passing through said bushing, a contact arm mounted on said control shaft, an arcuate wire-Wound resistance element placed inside the cylindrical wall of the casing, one or more soldering lugs having their inner ends next to the windings, an annular insulation plug forced within said wire-wound strip, a stop arm mounted at the end of the control shaft, and a closure for the open end of the casing, said closure having a stop cooperating with said stop arm.

3. A variable resistor comprising a. cylindrical casing closed at one end and open at the other end, a bushing secured to the closed end, a control shaft passing through said bushing, a contact arm and hub insulatedly mounted on the inner end of said control shaft, an arcuate wirewound resistance element placed inside the cylindrical wall of the casing, one or more soldering lugs having their inner ends next to the windings, an annular insulation plug forced within said wire-wound strip, another soldering lug passing beneath said plug and bearing at its inner end against said hub, a stop arm mounted at the end of the control shaft, and a closure for the open end of the casing, said closure having a stop lug cooperating with said stop arm.

4. A variable resistor comprising a cylindrical casing closed at one end and open at the other end, a bushing secured to the closed end, a control shaft passing through said bushing, a contact arm and metallic hub insulatedly mounted on the inner end of said control shaft, an arcuate wire-wound vresistance element placed inside the cylindrical wall of the casing, one or more soldering lugs having their inner ends interposed between Athe windings and the casing, an

annular insulation plug forced within said'wireber bearing against the aforesaid hub, a stop arm mounted at the end of the control shaft, a closure for the open end of the casing, said closure having a stop cooperating with said stop arm, and a single assembly screw passing through said casing, plug, and closure, said screw being so located as not to interfere with the desired range of movement of the contact arm.

5. A variable resistor comprising a continuous wire-wound resistance element, a contact movable thereover, and an insulation support external of the elements and forced against the outside of said element, said support being coated with a conductive coating contacting with a part of said element.

6. A variable resistor comprising a cylindrical casing wall, an arcuate wire-wound resistance strip carried within said wall, and a circular insulation plug forced within said arcuate resistance element, a part of the periphery of the plug being coated with a conductive coating.

'1. A variable resistor comprising a cylindrical casing wall, an arcuate resistance element carried within said wall, and a circular insulation plug forced within said arcuate resistance element. the periphery of the plug at oneend of the element being coated lwith a metallic coating ,in order'to short-circuit a part of the element.

- lugs and the metallic coating into contact with resistance element and an insulation plug forced within said arcuate resistance element, the periphery of the plug at one end of the wirewound element being coated with a metallic coating in order to short-circuit a part of the element. said plug acting to force the soldering the resistance element.

9. A variable resistor comprising a cylindrical casing wall, an arcuate wire-wound resistance strip carried within said wall, and a circular insulation plug forced within said arcuate resist ance element. the periphery of the plug at one `end of the wire-wound element being coated for a substantial distance with a metallic coating in order to short-circuit a part of the element, a contact arm for varying the resistance, a power switch, and means associated with the contact arm for operating the power switch while the contact arm is at the short-circuid end of the element.

10. A variable resistor comprising a cylindrical casing wall, an arcuate wire-wound resistance strip carried within vsaid wall, one or more soldering lugs having their inner ends interposed be tween the resistance element and the cylindrical wall. a circular insulation plug forced within said arcuate resistance element, the periphery of the y plug at one end of the wire-wound element being coated with a metallic coating for a substantialdistance in order to short-circuit a part of the element,a contact arm for varying the resistance, a power switch, and means associated with the contact arm for operating the power switch while the contact arm is at the shortcircuited end of the element.

1l. A variable resistor comprising a cylindrical casing wall, an arcuate wire-wound resistance element carried within said wall, and acirculari insulation plug forced within said arcuate resistance element, a portion of the periphery of said plug being coated with a carbonaceous resistance film whereby a part of the element is given a different resistance value than the remainder of the. element.

12. A variable resistor comprising a cylindrical casing wall, an arcuate wire-bound resistance element carried within said wall. one or more soldering lugs having their inner ends next to the resistance element, and a circular insulation plug forced within said arcuate resistance element, a portion of the periphery of said plug being coated witha carbonaceous` resistance illm whereby a .part of the element is given a different resistance value than the remainder oi' the element, said plug acting toforce the soldering lugs and the resistance film into contact with the resistance element.

13. A variable resistor comprising a cylindrical casing wall, an arcuate wire-wound resistance strip carried within said wall. one or more soldering lugs having their inner ends interposed between the resistance element and the cylindrical wall. and a circular insulation plug forced` within said arcuate resistance elementfin order to bind the wire windings in place and `in order to force the windings and soldering lugs into good electrical contact, a portion of the periphery of said plug being coated with a low resistance film whereby a part of the' resistance element is given a different resistance value than the remainder of the element.

14. A variable resistor comprising a cylindrical casing closed at one end and open at the other end, a bushing secured to the closed end, a control shaft passing through said bushing, a contact arm mounted on said control shaft, an arcuate wire-wound resistance element placed in side the cylindrical wall of the casing, an annular insulation plug forced within said wirewound strip, the periphery of said plug at one 15. A variable resistor comprisingA a cylindrical casing closed at one end and open at the other end, a bushing secured to the closed end, a control shaft passing through said bushing, a contact arm mounted on the control shaft, an arcu ate wire-wound resistance element placed inside the cylindrical 4wall of the casing, on'e or more soldering lugs having their inner ends interposed between the windings and the casing, an annular insulation plug forced Within said wire-wound strip, the periphery of said plug at one end of the wire-wound element being coated for a substantial distance with a metallic coating, a stop arm mounted at the nend of the control shaft, a closure for the open end of the casing, said closure including a power switch adapted to be operated by said stop arm, the parts being so proportioned that the switch is operated while the arm is at the metallic coated part of the plug. f

16. A non-uniform variable resistor comprising a uniform wire-wound resistance element including an insulation core and a uniform resistance wire wound thereon, an insulation support wall bearing against said element, a part of said wall 'being coated with a carbonaceous resistance nlm in order to give part of the wire-wound element al different `resistance value than the remainder of the element.

17. A variable resistor comprising a one-piece casinghaving an end anda cylindrical side wall, a bushing secured to said end, a control shaft passing through said bushing, an arcuately bent resilient contact arm mounted on said control shaft, an arcuate wire-wound resistance element' placed inside the cylindrical wall of the casing. said resistance element being small in radial dimension but broad in axial direction, said cylindrical side wall having an axial breadth greater than that of the resistance element, soldering lugs projecting outwardly from said casing and having their inner ends bent to lie between the outside of the resistance element and the inside of the cylindrical wall of the casing, a rigid annular insulation plug forced within the wirewound element to hold the same tightly against the soldering lugs and the cylindrical wall of the casing, said plug being substantially smaller in axial dimension than theV element and bearing against the forward part of the inner wall of the element, said contact arm bearing against -the remainder of the inner wall of said. element in back of said plug, and a removable closure for closing the open back end of the casing.

HENRY G. RICHTER. 

